This invention relates to a non-contacting method and microwave apparatus for proximity detection, and more particularly to proximity detection based on the perturbation of evanescent electromagnetic fields by an object.
A variety of different types of proximity detectors are known, such as those based on capacitive effects. A particular application that requires a reliable, accurate, non-contacting technique for measuring relatively small distances at high temperatures is the measurement of clearances between the tips of rotating turbine blades and the casing in a jet engine. In a jet engine the blade tip-casing clearances must be kept small for high engine efficiency. It is desirable to monitor the separation as it may change catastrophically with thermal variations. For such jet engine applications, the difficulty with a microwave system in which the phase shift of a propagating wave reflected off the blade tips is measured is that such a scheme suffers from multiple reflections of waves propagating throughout the closed engine shell and finally returning to the receiver.
The present invention is directed to a microwave proximity detector with quantitative output that radiates an insignificant amount of electromagnetic energy, and to the associated non-contacting method for detecting relatively small separation distances which is especially useful in those environments where little or no radiation loss can be tolerated.